The present invention pertains to directional filters and specifically to directional filters in the microwave or millimeter wave frequencies. Generally, a directional filter is a four port device with the ports being numbered clockwise, from an input port, one through four. Directional filters are well-known in the art and have been used for years in applications wherein a signal formed of a plurality of frequencies is applied to the input port and the operating or selected frequency is filtered out and available at port four. The remainder of the input signal (all of the unselected frequencies) is available at port two. A typical prior art directional filter is disclosed in U.S. Pat. No. 4,287,605, entitled "Directional Filter for Mixers, Converters and the Like", issued Sept. 1, 1981. The directional filter disclosed in this patent is large, relatively complicated to construct, and difficult to cascade to form channelized filter, and the like.